Field of the Invention
The present invention relates to a variable displacement axial piston device, and more particularly, relates to a variable displacement axial piston device with a trunnion type movable swash plate.
Related Art
In a variable displacement axial piston device that includes a cylinder block rotating around a rotational axis line, plural pistons accommodated in the cylinder block in a relatively non-rotatable manner around the axis line with respect thereto and in a reciprocating manner along the axis line, and a movable swash plate varying a reciprocating range of the plural pistons, a trunnion type movable swash plate has been widely used as the movable swash plate.
In more detail, the trunnion type movable swash plate includes a swash plate main body with which free end portions of the plural pistons engage, and a trunnion shaft that extends from the swash plate main body (see, for example, Japanese unexamined patent application publication No. H11-201023).
A supporting member such as a housing that accommodates the cylinder block is provided with a bearing portion that is coaxially aligned with a slanting reference axis line of the movable swash plate, and the trunnion shaft is supported by the bearing portion in a rotatable manner.
The swash plate main body is subjected to thrust force from the plural pistons. In the trunnion type movable swash plate, the trust force is received by the trunnion shaft and the bearing portion.
Accordingly, if a rotating frictional resistance between the trunnion shaft and the bearing portion is large, a large operational force to slant the trunnion type movable swash plate is needed so that the movable swash plate is difficult to be slanted rapidly.
In particular, in a case where the axial piston device is utilized as a hydraulic pump device of a traveling HST (hydrostatic transmission) provided in a working vehicle and the movable swash plate is slanted within a slanting range inclusive of a neutral position, the movable swash plate is needed to be returned to the neutral position as quickly as possible in order to shorten a braking distance in which the working vehicle is shifted from a traveling state to a stopping state.